Apparatus for detecting surface discontinuities



Sept. 4, 1956 1-, DE FOREST EI'AL 2,761,997

APPARATUS FOR DETECTING SURFACE DISCONTINUITIES Original Filed Oct. '7,1946 fziz arzfar" 5 7, 45, 79 DEAF-5,6587

1751/0) A. S urs ilnited States PatentO APPARATUS FOR DETECTING SURFACEDISCONTINUITIES Taber de Forest, Northbrook, and Henry N. Staats,Chicage, Ill., assignors to Magnaflux Corporation, Chicago, 111., acorporation of Delaware Original application October 7,1946, Serial No.701,704. 136iit2iig and this application June 15, 1950, Serial No.

1 Claim. (Cl. 317-3) The present invention relates to an apparatus fordetecting surface discontinuities and more particularly to means forproducing a finely particulated cloud of electrostatically chargedparticles suspended in a fluid n edium.

This application is a division of our application of the same title,Serial No. 701,704, filed October 7, 1946, now U. S. Letters Patent2,515,396, issued July 18, 1950, and a continuation-in-part of ourapplication Serial No. 648,234, filed January 18, 1946, now U. S.Letters Patent No. 2,499,466, issued March- 7, 1950, both of saidapplications being assigned to the assignee of the instant invention.

We have found, as fully disclosed in the above identified applications,that surface discontinuities may be detected in poorly conductivearticles, such as glass botties, or the like, by first wetting thebottles with water or a Water-miscible liquid; drying the surfacesuperficially; introducing finely particulated electrostatic particlesonto the superficially dried surface; and finally observing anyconcentration of particulated material at the surface of the article.Under the conditions above outlined, electrostatically charged particlesaccumulate at or on any surface discontinuities, or cracks in thearticle in well-defined comparatively dense conglomeratio-ns which arecoextensive with the cracks. The resulting definite visual indicationnot only indicates the presence of cracks, but indicates the extent ofsuch defects.

The present invention now provides an improved apparatus for forming anelectrostatically charged cloud consisting of finely dividedparticulated material suspended in a fluid medium, preferably air. Thedevice disperses finely particulated material in a gaseous medium by theutilization of an aspirator, operating in accordance with the Bernoullieltect. The fluidsuspension of finely divided particles is then conveyedby suitable means to its point of use, an electrostatic charge beingimparted to the particles, as by passing the particle clouds through asuitable rubber hose and nozzle or the like.

it is, therefore, an important object of the present invention toprovide an improved apparatus for the de tection of surfacediscontinuities by the formation of a finely divided cloud ofelectrostatically charged particles and means for introducing theparticles onto an article to be tested.

Another important object of the present invention is to provideaspirator means for forming a suspension of finely particulated solidmaterial in a fluid and imparting an electrostatic charge to theparticles while so suspended.

It is a further important object of the present invention to provide anapparatus for the detection of surface discontinuities in anelectrically non-conductive material, including means for utilizing theBernoulli eflect to form a suspension of finely particulated solidmaterial in a fluid, directing the suspension against an article to betested, and imparting an electrostatic charge to the suspensionparticles.

It is a still further important object of the present invention toprovide an improved apparatus for forming a suspension ofelectrostatically charged solid particles in a fluid, includingaspirator means for forming the suspension of solid material in a fluidstream, and anonconductive nozzle for directing the suspension againstan article to be tested, the nozzle serving to impart to particlespassing therethrough an electrostatic charge.

Other and further important objects of this invention will be apparentfrom the disclosures in the specification and accompanying drawings.

On the drawings:

Figure 1 is a side elevational view, with parts broken away and insection of apparatus of the present invention;

Figure 2 is a longitudinal sectional view of a modified form of nozzlefor use with the apparatus of Figure 1;

Figure 3 is an additional modified form of nozzle; and

Figure 4 is a sectional view of still another modified form of nozzle.

As shown on the drawings:

In Figure 1 reference numeral 10 refers generally to a containerofsuitable shape provided with closed bottom and side walls andcommunicating through its upper Wall 11 with an upwardly diminishingpassage 12 communicating with a reduced outlet orifice 13. The container10 has disposed therein a body 14 of finely particulated solid material.In general the material i4 may be any finely divided solid, but we havefound it preferable to employ non-hygroscopic inorganic substancescapable of being highly charged electrostatically. Calcium carbonate, orprecipitated chalk, has thus far been found to be one of best materials.However, it is possible to employ talc, powdered mica, diatomaceousearth, clays such as kaolin, calcium sulfate, iron oxide, carbon black,aluminum powder, and many others.

The body 14 of particulated solid material within the container 10 issurmounted by a float plate 15 centrally apertured, as at 16, to receivea conduit or tube 1"] which in turn telescopically receives an upwardlyextending flexible conduit or hose 18 formed of rubber or the like whichextends through one of the side walls of the container 10 forcommunication with a source of fluid, such as air, under pressurethrough a supply pipe 19 and a valve 20. The valve 20 communicates witha T fitting 21 in the supply line 19, and it will be seen that uponopening the valve 20 a charge of fluid under pressure is introduced intothe container 10 directly upon the material 14 therein so that thematerial is agitated and will become suspended in fluid entering thecontainer through the line 18. The supply line 19 is provided with asecond valve 22 located therein beyond the T-fitting 21, and the valve22 is adapted to admit air under pressure into a reduced conduit 23coaxial with and interiorly of an adapter fitting 24. The adapterfitting 24 is provided with an intermediate depending reduced diameterconduit 24a which communicates with the reduced orifice 13 of the outletpassage 12 of the container 10 hereinbefore described. The conduit 23receiving air under pressure therethrough is supported in coaxialrelation with the fitting 24 by means of a block 23a interposedtherebetween, and the conduit 23 extends axially of the fitting 24 fromthe valve 22 to a point beyond the depending conduit 25.

It will be appreciated by those skilled in the art that the cooperatingconduit 23 and the fitting 24 will function as an aspirator to produce areduced pressure at the orifice 13 in accordance with the Bernoullieffect, and this reduced pressure will serve to draw the suspension ofsolids influid from'the container 14 into the fitting 24. The cloud ofsuspended, finely particulated solid matter thus formed in the fitting24 .is conducted through a flexible conduit 25 which may be rubber to apair of branched conduits 26 which-alsomay be rubber disposedimmediately adjacent the upper portion of anarticle A to be tested. Thebranched conduits 26 each terminate in a nozzle 27 immediately adjacentthe article A.

The nozzles 27 each comprise a pair-of coaxial, axially extendingstepped chambers 28 and 29, the larger of the chambers (29) receivingthe-particulated cloud from the chamber 28 and'the conduit 26. Thenozzles 2'7 are preferably constructed ofhard rubber to produce anelectrostatic' charge in the suspended solid matter of the cloudintroduced therethrough as hereinbefore explained. Alternately,thenozzles may be made of phenol-tonnaldehyde resin, wood, paper, ethylcellulose resin, or other similar materials capable of so producing anelectrostatic charge.

In that form of nozzle illustrated in Figure 2, the stepped bores 28 and29 arereplaced by a single tapering bore 30 of increasing diametertoward the article A. In Figure 3 the nozzle 27 is formed of a firstnozzle block 31 receiving the conduit 26 and a second cylindrical block32 telescopically fitted over the nozzle block 31. The nozzle block 31is provided with an interior, generally cylindrical recess 33 and thenozzle 32 is pro vided with an internal axial bore 34 of greaterdiameter than the recess 33.

In Figure 4 of the drawings, the nozzle 27 is substantially identicalwith that hereinbefore illustrated and described in Figure l with theaddition of a terminal deflector block 35 telescopically mounted on thenozzle block 27 and provided with the downturned deflector tip 36.

The purpose of the stepped bores, or the frusto-conical bore of theembodiment of Figure 2, is to produce a spraying nozzle action touniformly distribute the pewdered cloud acting through the nozzle overthe surface of the article A to be tested. In the embodiment of Figure3, the telescoping adjustment of the nozzle sleeve 32 relative to theblock 31 makes possible the adjustment of the angle of the spray,thereby accommodating the employment of this form of nozzle to varioussizes and types of articles being tested. In the embodiment of Figure 4,the deflector plate 36 insures the direction of the electrostatic cloudeither along the entire length of the article A to be tested or to aspecific portion of the article. It will be appreciated that thedeflector block 35 is telescopically mounted on the nozzle 27 for axialadjustment for varying the angle of the spray and the location to whichit is deflected.

From the foregoing description, it will be appreciated thatthepresent-invention provides novel means for form ing a cloud ofelectrostatically charged solid particles suspended in a fluid medium.Obviously, for most applications it is desirable to employ compressedair for economic reasons. However, any suitable fluid under pressure maybe employed as desired.

It will be understood that modifications and variations may be eifectedWithout departing from the scope of the novel concepts of the presentinvention.

2 claim as my invention:

An apparatus for spraying electrostatically charged particles over awetted surface of glass or the like to deect surfacediscontinuities, aconduit of electrical insulation material for a pressurized fluid mediumhaving finely divided particulate materialdispersed therein, and anozzle also of electrical insulation material on said conduit fordirecting the fluid medium and particulate material against thesurfaceofan article under test, said nozzle being formed of adjustabletelescoping portions defining a cylindrical inlet chamber and acylindrical outlet chamber having a diameter substantially greater thanthe diameter of said inlet chamber, for obtaining increased turbulencein the fluid medium and increased frictional contact-of the particleswith the interior surface of said nozzlewhile reducing the velocity ofthe fluid stream.

References Cited in the file of this patent UNITED STATES PATENTS1,349,751 Cross Aug. 17, 1920 1,736,969 Greiser Nov. 26, 1929 1,928,963Chafiee Oct. 3, 1933 2,058,218 Duccini et a1. Oct. 20, 1936 2,091,055Roselund et a1. Aug. 24, 1937 2,114,682 Gumaer Apr. 19, 1938 2,165,946Smith July ll, 1939 2,297,791 Ness Oct. 6, 1942 2,302,185 Campbell Nov.17, 1942 2,396,533 Root Mar. 12, D46 2,477,947 Yadoff Aug. 2, 19492,590,534 Hampe Mar. 25, i952 2,657,339 Hampe Oct. 27, 1953 2,659,841Hampe Nov. 17, 1953 OTHER REFERENCES Static Electricity, U. S. Dept. ofCommerce, National Bureau of Standards, Circular C438.

